Topological characterization of flow structures in resistive pressure-gradient-driven turbulence

9 pages, 13 figures.-- PACS nrs.: 52.35.Ra, 52.65.Kj, 47.27.−i.-- ArXiv pre-print available at: http://arxiv.org/abs/0811.3548Visualization of turbulent flows is a powerful tool to help understand the turbulence dynamics and induced transport. However, it does not provide a quantitative description of the observed structures. In this paper, an approach to characterize quantitatively the topology of the flows is given. The technique, which can be applied to any type of turbulence dynamics, is illustrated through the example of resistive ballooning instabilities.One of us (B.A.C.) is grateful to the Asociación EURATOM-CIEMAT for providing travel expenses. Part of this work is supported by the DGI (Dirección General de Investigación) of Spain under Project No. ENE2006-15244-C03-01 and by Grant No. CM-UC3M (Comunidad de Madrid—Universidad Carlos III) Project No. CCG07-UC3M/ESP-3407.Publicad

Topological characterization of the transition from laminar regime to fully developed turbulence in the resistive pressure-gradient-driven turbulence model

11 pages, 20 figures.-- PACS nrs.: 52.35.Ra, 52.65.Kj, 47.27.−i.For the resistive pressure-gradient-driven turbulence model, the transition from laminar regime to fully developed turbulence is not simple and goes through several phases. For low values of the plasma parameter β, a single quasicoherent structure forms. As β increases, several of these structures may emerge and in turn take the dominant role. Finally, at high β, fully developed turbulence with a broad spectrum is established. A suitable characterization of this transition can be given in terms of topological properties of the flow. Here, we analyze these properties that provide an understanding of the turbulence-induced transport and give a measure of the breaking of the homogeneity of the turbulence. To this end, an approach is developed that allows discriminating between topological properties of plasma turbulence flows that are relevant to the transport dynamics and the ones that are not. This is done using computational homology tools and leads to a faster convergence of numerical results for a fixed level of resolution than previously presented in Phys. Rev. E 78, 066402 (2008).Part of this research was sponsored by the Dirección General de Investigación of Spain under Project No. ENE2006-15244-C03-01. One of us (BAC) is grateful for the "Cátedra de Excelencia" from Universidad Carlos III and Banco Santander. The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Barcelona Supercomputing Center—Centro Nacional de Supercomputación (http:// www.bsc.es).Publicad

Characterization of nondiffusive transport in plasma turbulence via a novel Lagrangian method

4 pages, 3 figures.-- PACS nrs.: 52.35.Ra, 05.40.Fb, 47.27.−i, 52.65.Kj.A novel method to probe and characterize the nature of the transport of passive scalars carried out by a turbulent flow is introduced. It requires the determination of two exponents which encapsulate the statistical and correlation properties of the component of interest of the Lagrangian velocities of the flow. Numerical simulations of a magnetically confined, near-critical turbulent plasma, known to exhibit superdiffusive radial transport, are used to illustrate the method. It is shown that the method can easily detect the change in the dynamics of the radial transport that takes place after adding to the simulations a (subdominant) diffusive channel of tunable strength.Research supported by Spanish DGES Grant No. ENE2006-15244-C03-01/FTN and DOE Office of Science Grant No. DE-FG02-04ER54741 at University of Alaska. ORNL researchers sponsored by U.S. DOE under Contract No. DE-AC05-00OR22725.Publicad

Nature of Transport across Sheared Zonal Flows in Electrostatic Ion-Temperature-Gradient Gyrokinetic Plasma Turbulence

4 pages, 4 figures.-- PACS nrs.: 52.35.Ra, 05.40.Fb, 52.55.Fa, 52.65.Tt.It is shown that the usual picture for the suppression of turbulent transport across a stable sheared flow based on a reduction of diffusive transport coefficients is, by itself, incomplete. By means of toroidal gyrokinetic simulations of electrostatic, collisionless ion-temperature-gradient turbulence, it is found that the nature of the transport is altered fundamentally, changing from diffusive to anticorrelated and subdiffusive. Additionally, whenever the flows are self-consistently driven by turbulence, the transport gains an additional non-Gaussian character. These results suggest that a description of transport across sheared flows using effective diffusivities is oversimplified.Research carried out at ORNL, managed by UT-Battelle LLC, for US DOE under Contract No. DE-AC05-00OR22725. Research funded by DOE Office of Science Grants No. DE-FG02-04ER54741 at University of Alaska and No. DE-FG02-04ER54740 at UCLA.Publicad

Analysis of the blackout risk reduction when segmenting large power systems using lines with controllable power flow

Large electrical transmission networks are susceptible to undergo very large blackouts due to cascading failures, with a very large associated economical cost. In this work we propose segmenting large power grids using controllable lines, such as high-voltage direct-current lines, to reduce the risk of blackouts. The method consists in modifying the power flowing through the lines interconnecting different zones during cascading failures in order to minimize the load shed. As a result, the segmented grids have a substantially lower risk of blackouts than the original network, with reductions up to 60% in some cases. The control method is shown to be specially efficient in reducing blackouts affecting more than one zone.DG and PC acknowledge funding from project PACSS RTI2018-093732-B-C22 and APASOS PID2021-122256NB-C22 of the MCIN/AEI/10.13039/501100011033/ and by EU through FEDER funds (A way to make Europe), from the Maria de Maeztu program MDM-2017-0711 of the MCIN/AEI/10.13039/501100011033/, and also from the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 957852, VPP4Islands). B.A.C. and J.M.R.-B. acknowledge access to Uranus, a supercomputer cluster located at Universidad Carlos III de Madrid (Spain) funded jointly by EU FEDER funds and by the Spanish Government via the National Research Project Nos. UNC313-4E-2361, ENE2009-12213-C03-03, ENE2012-33219, and ENE2012-31753. OGB was supported in part by FEDER/Ministerio de Ciencia, Innovacion y Universidades - Agencia Estatal de Investigación, Project RTI2018-095429-B-I00 and in part by FI-AGAUR Research Fellowship Program, Generalitat de Catalunya. The work of OGB is supported by the ICREA Academia program